The present invention relates to a fuel injection nozzle for injecting highly-pressurized fuel into the combustion chamber in the internal combustion engine such as a diesel engine.
The fuel injection nozzle of this type was disclosed in U.S. Pat. No. 4,349,152 and Japanese Patent Disclosure No. 85,433/85. These well-known fuel injection nozzles are provided with accumulating chambers defined in their bodies, into which highly-pressurized fuel fed from the fuel injection pumps is introduced. When the highly-pressurized fuel is introduced into the accumulating chamber, pressure in the valve chamber of the body which is communicated with the accumulating chamber is also raised. Therefore, the nozzle needle is lifted by this pressure in the valve chamber and fuel in the accumulating and valve chambers is thus injected through the injection hole.
In the case of these above-described fuel injection nozzles of the pressure accumulation type, however, the fuel injection is attained using the accumulated energy of fuel filled in the accumulating chamber. Therefore, pressure in the accumulating chamber is maximum at the start of the fuel injection, then lowers gradually, and is minimum at the end of the fuel injection. In other words, the nozzle needle opens the injection hole to the maximum degree at the start of the fuel injection and then gradually makes it smaller. As a result, fuel injection ratio is maximum at the start of the fuel injection, and then gradually decreases toward the end of the fuel injection. Combustion pressure in the combustion chamber rises rapidly to thereby increase combustion sound and engine noise. In addition, temperature in the combustion chamber rises rapidly to thereby increase the amount of NO.sub.x generated.